Crystal structure and microwave dielectric properties of Alkaline-Earth Hafnates, AHfO3(A=Ba, Sr, Ca)

FETEIRA, Antonio, SINCLAIR, Derek C., RAJAB, Khalid Z. and LANAGAN, Michael T. (2008). Crystal structure and microwave dielectric properties of Alkaline-Earth Hafnates, AHfO3(A=Ba, Sr, Ca). Journal of the American Ceramic Society, 91 (3), 893-901.

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Official URL: http://dx.doi.org/10.1111/j.1551-2916.2007.02134.x
Link to published version:: 10.1111/j.1551-2916.2007.02134.x

Abstract

The crystal structure and microwave (MW) dielectric properties of AHfO3 (A=Ba, Sr, and Ca) ceramics prepared by the solid-state route have been investigated. X-ray and electron diffraction show BaHfO3 to be an untilted cubic perovskite (a0a0a0, space group), whereas SrHfO3 and CaHfO3 are both orthorhombically distorted perovskites (a−b+a−, space group Pnma). AHfO3 ceramics with a relative density ∼90% of the theoretical X-ray density and microstructures consisting of randomly oriented equiaxed grains were prepared by firing at 1750°C for 6 h. Conventional transmission electron microscopy reveals the occurrence of long parallel ferroelastic domains in the subgrain microstructure of CaHfO3 and SrHfO3. At room temperature and MW frequencies, AHfO3 ceramics, where A=Ba, Sr, and Ca, have ɛr∼24.2, Q×fr∼14 250 GHz (at 8.9 GHz) and τf∼+111 ppm/K; ɛr∼23.5, Q×fr∼33 534 GHz (at 9.3 GHz), and τf∼−63 ppm/K; and ɛr∼21.4, Q×fr∼15 950 GHz (at 8.9 GHz), and τf∼−33 ppm/K, respectively. The ion polarizability for Hf4+ in a cubic perovskite environment is calculated to be 3.32 Å3, whereas in a noncubic environment it increases to 4.36–4.47 Å3. Finally, the dielectric properties of AHfO3 (A=Ba, Sr, and Ca) are compared with their titanate and zirconate counterparts.

Item Type: Article
Research Institute, Centre or Group: Materials and Engineering Research Institute > Structural Materials and Integrity Research Centre > Centre for Corrosion Technology
Identification Number: 10.1111/j.1551-2916.2007.02134.x
Depositing User: Hilary Ridgway
Date Deposited: 06 Jun 2012 15:54
Last Modified: 06 Jun 2012 15:54
URI: http://shura.shu.ac.uk/id/eprint/5330

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